Typo fixed

whatisterrain/whatisterrain.tex

@@ -155,7 +155,7 @@ \subsection{Strategy \#1: points + global interpolation function}
 This strategy is used because one can compactly represent a field (only the samples and a few parameters need to be stored).
 
 Notice that this strategy permits us to reconstruct the continuity of a terrain from the samples by calculating the value of the elevation, but that this value is \emph{not} persistently stored in memory.
-It is therefore less used in practice than the next strategy, which allows us to permanently store the terrain in a file and avoids us recomputing every time al the needed elevation values.
+It is therefore less used in practice than the next strategy, which allows us to permanently store the terrain in a file and avoids us recomputing every time all the needed elevation values.
 
 
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